Construction of Macroporous β-Glucosidase@MOFs by a Metal Competitive Coordination and Oxidation Strategy for Efficient Cellulose Conversion at 120 °C

Abstract

Metal–organic frameworks (MOFs) have become promising accommodation for enzyme immobilization in recent years. However, the microporous nature of MOFs affects the accessibility of large molecules, resulting in a significant decline in biocatalysis efficiency. Herein, a novel strategy is reported to construct macroporous MOFs by metal competitive coordination and oxidation with induced defect structure using a transition metal (Fe2+) as a functional site. The feasibility of in situ encapsulating β-glucosidase (β-G) within the developed macroporous MOFs endows an enzyme complex (β-G@MOF-Fe) with remarkably enhanced synergistic catalysis ability. The 24 h hydrolysis rate of β-G@MOF-Fe (with respect to cellobiose) is as high as approximately 99.8%, almost 32.2 times that of free β-G (3.1%). Especially, the macromolecular cellulose conversion rate of β-G@MOF-Fe reached 90% at 64 h, while that of β-G@MOFs (most micropores) was only 50%. This improvement resulting from the expansion of pores (significantly increased at 50–100 nm) can provide enough space for the hosted biomacromolecules and accelerate the diffusion rate of reactants. Furthermore, unexpectedly, the constructed β-G@MOF-Fe showed a superior heat resistance of up to 120 °C, attributing to the new strong coordination bond (Fe2+–N) formation through the metal competitive coordination. Therefore, this study offers new insights to solve the problem of the high-temperature macromolecular substrate encountered in the actual reaction.

Enhancing cellulose hydrolysis via cellulase immobilization on zeolitic imidazolate frameworks using physical adsorption

“…Furthermore, the residual enzyme activity after 5 cycles of reuse in this study reached 82.43% and 85.14%, also surpassing most of the prior research. It is noteworthy that, compared to our previous study [24] where cellulase was immobilized using the cross-linking method (with a loading of 359.89 mg/g), this research demonstrates a relatively lower enzyme loading. However, the activity of 71.39% surpasses the previous 69.35%.…”

Reactivity of metal–oxo clusters towards biomolecules: from discrete polyoxometalates to metal–organic frameworks

“…, high temperature), with the benefit of enzyme heterogenization. 49,303,304 However, to the best of our knowledge, MOC-based MOFs have not been reported for this purpose. Nevertheless, Zr- and Hf-based MOCs could be interesting for these applications as the synergy between the reactivity of the MOCs and that of the encapsulated enzyme may produce particularly effective catalysts.…”

“…302 Various MOF structures have already been used to encapsulate and stabilize b-glucosidase for hydrolysis of cellulose in conditions that would otherwise be detrimental to the protein structure (e.g., high temperature), with the benefit of enzyme heterogenization. 49,303,304 However, to the best of our knowledge, MOC-based MOFs have not been reported for this purpose. Nevertheless, Zr-and Hf-based MOCs could be interesting for these applications as the synergy between the reactivity of the MOCs and that of the encapsulated enzyme may produce particularly effective catalysts.…”

Enzyme immobilization in a Ru(N^N)3-modified covalent organic framework for photoenzymatic cascade catalysis

“…19,20 Their structural designability, high porosity, and periodic network make them ideal platforms for enzyme immobilization. [21][22][23] The crystalline nature and conjugation properties of COFs also make them promising candidates for photocatalytic platforms. [24][25][26][27][28] By tailoring building blocks or modifying the frameworks, the photophysical and photochemical properties of COFs can be ne-tuned.…”